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Present invention relates generally to power supplies technologies and specifically to the DC plasma supplies for a sputter deposition of material layers on a substrate, and it was originally disclosed in Provisional Patent Application No. 60/207,453 filed with US PTO on May 30, 2000.
DC plasma power supplies are used as sources of energy at a sputter deposition in the apparatuses, typically of a magnetron design, in the semiconductor industry. DC plasma power supplies are manufactured by the companies worldwide, including Advanced Energy Industries, Inc. of Fort Collins, Colo., USA.
Major drawbacks of the DC plasma power supplies of the prior art are intensive and repetitive arcing at plasma ignition and plasma termination and a need in the striking voltage to initiate a plasma in a sputtering apparatus of either magnetron or non-magnetron design.
Cumulative negative effects of the arcing are severe damage to substrates (wafers), caused by the induced particle contamination and soft X-rays, deterioration of electrical integrity of a sputtering apparatus and of a DC plasma power supply, and induced electromagnetic interference.
Plasma at arcing represents a short circuit and a DC plasma power supply generates at arcing the repetitive 0.1-10 microsecond pulses (surges) of the output current typically exceeding 10-100 times the nominal output current at a sputter deposition and reaching hundreds of amps. Repetition rate of these pulses may vary from 0.1 to 10-50 kHz. The surges of the output current result in micro-evaporation of the target material and in the particle contamination of a substrate.
The spikes of the output voltage of 1.5-2.5 kV accompany the surges of the current at arcing and these instabilities may last from several to hundreds of milliseconds. Arcing in a sputtering apparatus also results in release of the particles of different origin otherwise suspended by stable plasma off the perimeter of a substrate. At arcing these particles fall onto a substrate and contaminate it, representing one of the major sources of the yield losses at sputtering.
To initiate plasma a DC plasma power supply of the prior art produces a striking voltage, also typically in a range of 1.5-2.5 kV, and a striking voltage itself promotes arcing in a sputtering apparatus at plasma ignition.
Soft X-rays are generated at arcing by the spikes of the output voltage exceeding or about 1 kV, including the striking voltages, and they are detrimental to the dielectric layers on a substrate and also represent an environmental hazard.
High voltage spikes also deteriorate electrical integrity and reliability of a sputtering apparatus, specifically, of a cathode assembly. High voltage spikes and surge currents at arcing deteriorate electrical integrity and reliability of a DC plasma power supply of the prior art. They are also a source of AC and RF electrical interference for devices and instruments of a sputtering apparatus and of the other electronic systems. Arcing at plasma ignition and plasma termination tends to be supported by the energy stored in the DC plasma power supplies of the prior art. This phenomenon dictates use of the reactive components with the reduced nominal value in the output filters of these power supplies. It results in the less effective filtering and higher ripples of the output voltage and output current during a sputter deposition. These ripples themselves may promote various plasma instabilities and arcing at sputtering.
The invented DC plasma power supply provides plasma ignition and termination with no arcing regardless of the amount of energy stored in the power supply itself, offering more margins for better filtering and lower ripples at sputtering.
A DC plasma power supply of the present invention corrects the drawbacks of the prior art. Present invention is based on a theory of the plasmas, teaching that a DC plasma discharge becomes stable at the applied voltages greater than a specific voltage Vmin (Handbook of plasma processing technology, S. M. Rossnagel et al 1990, Noyes Publications, pp. 47-58; Industrial plasma engineering, J. R. Roth 1995, IOP Publishing, pp. 283-390; Handbook of sputter deposition technology, K. Wasa et al 1992, Noyes Publications, pp. 97-122; U.S. Pat. No. 6,190,512 Soft plasma ignition in plasma processing chambers).
Value of voltage Vmin depends on composition and pressure of the process gas(es), design properties of a sputtering target and a sputtering apparatus, and it can be measured prior to the processing of a product substrate.
Results of these measurements are used in the invented DC plasma power supply to define the settings for the arcing free plasma ignition and termination.
The invented DC plasma power supply effectively eliminates arcing, high voltage spikes, and soft X-ray radiation at plasma ignition and at plasma termination during a sputter deposition, and it does not require a striking voltage to initiate a plasma.
The invented DC plasma power supply reduces particle contamination and damage to a substrate at a sputter deposition. It also increases electrical integrity of a sputtering apparatus and its own electrical integrity by limiting the output voltages and output currents to the values required for sputtering. It also reduces the AC and RF electrical interference and a soft X-ray hazard.
These and other advantages of the invented DC plasma power supply are achieved by means of preventing exposure of the process gas(es) at sputtering to the output voltages lower than Vmin, by means of dynamic control of the mode of operation, and by means of controlled and gradual transitions from a gaseous state to a plasma state and from a plasma state to a gaseous state in a sputtering apparatus.
It is objective of the present invention to increase yield at a sputter deposition by eliminating arcing in a sputtering apparatus at plasma ignition and termination.
It is another objective of the present invention to increase electrical integrity of a sputtering apparatus.
It is another objective of the present invention to increase electrical integrity of a DC plasma power supply.
It is another objective of the present invention to reduce the AC and RF electromagnetic interference and the soft X-ray hazard caused by arcing at plasma ignition and termination.
It is another objective of the present invention to reduce limitation to filtering of the ripples of the output voltage and output current of a DC plasma power supply.
The invention is particularly useful in production by means of a sputter deposition of the Very Large Scale Integration (VLSI) devices in the semiconductor industry, optical and magneto-optical media, ultra thin film magnetic heads for computer hard drives, and in other related industries.
The above and other objectives and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.